test-in-docker: quickly test frameworks in docker

This adds `./test-in-docker` for quickly playing with various frameworks.

All the containers are based off Ubuntu 14.04 which has ZSH 5.0.2.

Thanks to @dritter for figuring out all the framework installation
methods.

docker/antigen/Dockerfile

@@ -0,0 +1,7 @@
+FROM p9k:base
+
+COPY docker/antigen/install.zsh /tmp/
+RUN zsh /tmp/install.zsh
+
+COPY ./ p9k/
+COPY docker/antigen/zshrc .zshrc

docker/antigen/install.zsh

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+#!/bin/zsh
+
+mkdir ~/antigen
+
+curl \
+  -qLsSf \
+  -o ~/antigen/antigen.zsh \
+  https://git.io/antigen
+
+source ~/antigen/antigen.zsh
+
+# EOF

docker/antigen/zshrc

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+source ~/antigen/antigen.zsh
+
+antigen theme "${HOME}/p9k" powerlevel9k --no-local-clone
+antigen apply